Process for rendering normally flammable cellulosic articles fire retardant



2 992 942 PROCESS FOR RENnERflsG NORMALLY FLAM- liA lNAjliLE CELLULOSIC ARTICLES FIRE RETARD- Robert R. Dreisbach and John L. Dang, Midland, Mich., assignors to The Dow Chemical Company, Midland, M1ch., a corporation of Delaware No Drawing. Filed May 31, 1957, Ser. No. 662,600 6 Claims. (Cl. 117-137) This invention relates to a process for producing a fire retardant cellulosic article and particularly to a composition exhibiting a reduced tendency to afterglow.

This application is a continuation-in-part of U.S. Serial No. 459,850, filed October 1, 1954, now US. 2,793,874.

tates Patent i For the purposes of this application, the term cellulosic article means a material comprising natural or regenerated celluloses and mixtures thereof, and the textiles comprising fibers of such cellulosic materials. By fire retardant is meant a material treated so that it is resistant to the propagation of flame across its surface after the igniting flame has been removed or burns very slowly after the flame has been removed.

Various compounds and compositions have been used or suggested for use in processes for treating cellulosic and other normally flammable organic materials to render them resistant to flame and to prevent afterglow. Many of the proposed compounds contain nitrogen or phosphorus, or both. Thus, in US. Patent 2,574,518, the use of brominated dialkene amido phosphates has been disclosed. Also, in US. Patent 2,305,035 is disclosed the use of alkylolamine guanidines. 525, melamine pyrophosphate is used as a flameproofing agent. The use of polyphosphorylamide is disclosed in US. Patent 2,596,936. For a description of further compounds and compositions, reference may be made to Little, Flameproofing Textile Fabrics, Reinhold Publishing Corporation, New York (1947).

The compositions or treatments that are used in textile fabrics to make such fabrics resistant to flame may be classified generally into two groups; (1) temporary or non-durable, in which the fire retarding agent is likely to be removed by washing, and (2) durable, in which the fire retarding agent is not removed by washing.

The compounds that have been used in the past to give a durable fire retardant treatment to cellulosic fabrics have suffered from the disadvantage that after treatment the fibers become hard and brittle and cannot be folded Without breaking. In addition, such compounds frequently weaken the fiber and thus limit its usefulness. Many of these prior compounds prohibitively increase the cost of the articles.

It is accordingly an object of this invention to provide a process for rendering normally flammable cellulosic articles, especially textile goods, permanently fire retardant.

It is a further object to provide a process for rendering cellulosic articles permanently fire retardant that will not appreciably alter the desirable characteristics of the cellulosic material.

Another object is to provide a process by which a cellulosic article may be treated to prevent any afterglow after the flames are extinguished.

It is a still further object to provide a fire retardant cellulosic article.

The above and related objects are accomplished by a process in which a normally flammable cellulosic article is impregnated with polyvinylpyridine and phosphoric acid in certain proportions followed by a rinse with a dilute aqueous alkaline solution to neutralize any acidity. Articles treated according to the process of this invention In U.S. Patent 2,418;

2,992,942 Patented July 18, 1961 "ice show the properties of being both self-extinguishing when the source of ignition is removed and exhibiting no tendency to afterglow after the flames have been extinguished. The tensile strengths of the treated articles show significantly less reduction than those treated by the prior processes.

Polyvinylpyridine is conveniently prepared in the form of a latex by polymerizing vinyl pyridine in aqueous emulsion, and when thus prepared the latex may be used to impregnate the cellulosic article directly followed by treatment with phosphoric acid or the latex may be acidified with phosphoric acid and the cellulosic article impregnated with the acidified latex. Great care must be exercised in both of those procedures however, so that the latex does not coagulate prematurely, and that the cloth is thoroughly impregnated.

It is preferred to coagulate a polyvinylpyridine latex so as to recover the polymer and to impregnate the cloth from an aqueous acidic solution of the polyvinylpyridine.

It is more convenient to transport and to store the solid polymer than it is the latexes. It is easier to obtain a constant amount of polyvinylpyridinium phosphate on the cloth using solutions instead of latexes.

The amounts of polyvinylpyridine and phosphoric acid which can be employed effectively may be varied within wide limits, although the weight ratio of ingredients must be such that there is at least 2 parts of polyvinylpyridine for each part of phosphoric acid and such ratio of 2 to 1 is the preferred treatment. Also, it is necessary that the treated fabric contain after drying at least 0.5 percent of phosphorus. When there is used more than the above stated proportion of phosphoric acid, the increased acidity is so great as to reduce the tensile strength of the treated article beyond that at which the treated article may have any usefulness. For example, when the polyvinylpyridine and the phosphoric acid are used in a 1 to 1 Weight ratio, this tensile strength degradation is so great that the treated article has only 25 percent of the strength of the original article before treatment. The reduction occurs during the heat-setting step and if the impregnant is too acid at that time, no amount of after rinse will prevent the tensile strength degradation.

When appreciably less than the above stated 2 to 1 weight proportion of phosphoric acid is used, the treated article will exhibit afterglow after the source of flame ignition is removed and the fire extinguished. Afterglow represents one of the most serious problems in the extinguishing of any fire involving cellulosics. Any fire retardant which does not prevent afterglow is of little utility as a fabric impregnant.

In addition, it has been found that the treated fabric should contain at least 0.5 weight percent of phosphorus to be non-afterglowing. It is preferable to have at least 1.0 weight percent of phosphorus incorporated into the treated article, so that even though some of the impregnant may be lost through abrasion or other means during subsequent handling operations, the treated fabric will remain self-extinguishing and non-afterglowing.

To prevent the possibility of any free excess phosphoric acid remaining on the cloth, the impregnated article is neutralized with a dilute aqueous alkaline solution, such as dilute ammonium hydroxide or dilute sodium hydroxide. After drying, any adherent inorganic phosphate may be brushed, washed or shaken from the cloth. Following the neutralization with the dilute alkaline solution, the impregnant is set by heating for a shoit time at a temperature of from C. to C. Below 100 C. the heating requires a long time and appreciably above 160 C. the treated fabric is degraded.

The durability of the present treatment is due to the formation and setting of polyvinylpyridinium phosphate which is intimately distributed throughout the cellulosic article. The treated article may be washed or laundered repeatedly without losing its valuable fire retardant properties.

The operation of the process of the invention will be more apparent from the following illustrative examples.

Example 1 A sample of number 140 cotton sheeting was immersed in a latex of polyvinylpyridine, containing 10 percent polymer solids, allowed to drain, and air dried. The sheeting was rinsed with a 10 percent phosphoric acid solution, allowed to drain, and air dried. Finally, the sheeting was rinsed with a dilute ammonium hydroxide solution, air dried, and then heated for twenty minutes at 100 C. When the so treated sheeting was subjected to a flame and then the flame removed, the sheeting was found to be self-extinguishing and exhibited no tendency to afterglow. After the sheeting was washed in hot, soapy water and dried, and again subjected to the flame it still was self-extinguishing and showed no afterglow.

Example 2 A sample of number 140 cotton sheeting was immersed in a latex of polyvinylpyridine containing 9 percent by Weight of polyvinylpyridine to give a 2:1 ratio of polyvinylpyridine to phosphoric acid acidified with percent of phosphoric acid. The sheeting was wrung dry, air dried, rinsed with dilute sodium hydroxide, air dried, and finally heated at 100 C. for /2 hour followed by heating at 150 C. for /2 hour. A second sample of sheeting was immersed in a methanol solution of urea and phosphoric acid in which the ratio of urea to acid was 3 to 1. The sheeting was then dried at 110 C. for /2 hour. A third sample of sheeting was left untreated to serve as a blank. All three samples were tested for tensile strength. The treatment of the present invention resulted in less than half as much reduction in strength of the cloth as was caused by the conventional urea-phosphoric acid treatment, and was durable through a greater number of laun derings in its flame retardant effect.

Example 3 A 4 percent aqueous solution of polyvinylpyridine was mixed with 2 percent of its weight of phosphoric acid. A sample of number 140 cotton sheeting was immersed in the solution, allowed to drain, and air dried. The treated sheeting was rinsed with a dilute alkaline solution and dried at 150 C. for 5 minutes. When subjected to the flame test, the cloth was found to be self-extinguishing and exhibited no afterglow. The sheeting could be laundered repeatedly and the fire retardant properties were not materially impaired.

Example 4 To demonstrate the need for employing the ingredients of the composition in the stated proportions, tests were conducted as follows: acidic aqueous solutions of polyvinylpyridine were prepared. One solution had a ratio of phosphoric acid to pyridine of about 0.89 to 1 and was used for purposes of comparison. The second solution had a ratio of phosphoric acid of 1 to 2 and represented the compositions of this invention. Two samples of number 140 cotton sheeting were impregnated with each solution. Each of the samples was rinsed with dilute ammonium hydroxide. One sample of cotton of each impregnant was air dried. The other samples were oven dried at 150 C. for /2 hour. When the oven dried samples were tested for tensile strength, it was found that the sample impregnated with the comparative solution had lost percent of its untreated strength whereas the sample impregnated with the solution of this invention had lost but 41 percent of its untreated strength.

All of the samples were laundered in hot detergent water for 5 minutes and then rinsed in hot and cold water and dried. It was found that both of the samples impregnated with the comparative solution burned and exhibited afterglow. The air dried sample of this invention did not burn but did exhibit afterglow. The oven dried sample of this invention did not burn and did not exhibit afterglow.

Example 5 The procedure of Example 4 was repeated except that the alkaline rinse was omitted. The samples after drying were both self-extinguishing and exhibited no afterglow. However, each of the samples was too weak to be able to be laundered without disintegration of the fabric.

The present method is applicable to wood, paper, rayon, cotton and other cellulosic products, especially those which are thin, flexible and absorbent.

The process is likewise operable when the polyvinylpyridine is prepared from 2-vinyl or 4-vinyl pyridine.

We claim:

1. The process which comprises impregnating from an aqueous vehicle a normally flammable cellulosic article with polyvinylpyridinium phosphate of composition that contains at least two parts of polyvinylpyridine for each part of phosphoric acid and in amounts to provide at least 0.5 percent by weight of phosphorus on the treated article, neutralizing any excess phosphoric acid by rinsing the so impregnated article with a dilute aqueous alkaline solution, and finally setting the polyvinylpyridinium phosphate impregnant on said article by heating to a temperature of from to C. for from 5 to 30 minutes.

2. The process claimed in claim 1 wherein the polyvinylpyridine and the phosphoric acid are applied to the article simultaneously from the same aqueous vehicle.

3. The process claimed in claim 1 wherein the polyvinylpyridine is applied to the article from an aqueous latex followed by treatment with phosphoric acid and subsequent neutralization with dilute alkaline solution.

'4. The process claimed in claim 1 wherein the polyvinylpyridine is applied to the article from an aqueous solution containing the requisite phosphoric acid followed by neutralization.

5. The process claimed in claim 1 wherein said normally flammable cellulosic article is a textile product.

6. The process claimed in claim 5 wherein said textile product is cotton cloth.

References Cited in the file of this patent UNITED STATES PATENTS Morgan Feb. 23, 1937 Pritchard Feb. 22, 1955 OTHER REFERENCES 

1. THE PROCESS WHICH COMPRISES IMPREGNATING FROM AN AQUEOUS VEHICLE A NORMALLY FLAMMABLE CELLULOSIC ARTICLE WITH POLYVINYLPYRIDINIUM PHOSPHATE OF COMPOSITION THAT CONTAINS AT LEAST TWO PARTS POLYVINYLPYRIDINE FOR EACH PART OF PHOSPHORIC ACID IN AMOUNTS TO PROVIDE AT LEAST 0.5 PERCENT BY WEIGHT OF PHOSPHOROUS ON THE TREATED ARTICLE, NEUTRALIZING AN EXCESS PHOSPHORIC ACID BY RINSING THE SO IMPREGNATED ARTICLE WITH A DILUTE AQUEOUS ALKALINE SOLUTION, AND FINALLY SETTING THE POLYVINYLPYRIDINIUM PHOSPHATE IMPREGNANT ON SAID ARTICLE BY HEATING TO A TEMPERATURE OF FROM 100* TO 160*C. FOR FROM 5 TO 30 MINUTES. 